This invention relates to an idler bearing-sealing device for a timing belt of an automotive engine, etc.
A conventional idler bearing for the timing belt of an automobile engine such as is shown in FIG. 11, is fabricated by, e.g., press fitting a sleeve 200 to the inner peripheral surface 101 of an inner ring 100, A mounting bracket 300 is press-fitted to the outer peripheral surface 201 of the sleeve 200. One end of the idler bearing is mated with a desired fixed part (not shown) by the bracket 300 and the other end thereof is fixed with a bolt inserting through a position-adjusting slot 302 formed in a blocking wall 301 at one end of the sleeve 200. The idler bearing can provide a belt with proper tension by changing its fitting position along the long position-adjusting slot 302.
Another idler bearing has recently been developed which has a sleeve incorporating an inner ring 401, shown in FIG. 12, to reduce the number of component parts, weight and cost.
An idler bearing must be sealed tightly when it is installed in an automobile because of oscillation resulting from vibrations, shocks or changes of the belt-feeding rate. For this reason, contact-type bifurcated sealing lips 501, 502 shown in FIGS. 13(a)-(c) are used very often. Grease often leaks out of these lips under vibration, however, because a bifurcated sealing lip such as 501 or 502 is installed with the gap between a lip portion 503 or 504 on the raceway side and the outer peripheral surface 402 of an inner ring. In the case of the lip of the type shown by 501, moreover, a lip extension 505 on the side opposite to the raceway is so arranged as to slidably contact a curved concavity 506. With this arrangement, grease life is shotened because the interference of the lip 505 becomes great, thus causing frictional heat generation. Furthermore, the lip 505 may adhere to the concavity 506 as the pressure in the bearing decreases when it is cooled, and this increases the torque. In the case of lips such as that shown as 507 in FIG. 13(c), the grease leakage is reduced and the intrusion of foreign matter is more effectively prevented in comparison with the lips 501, 502, because the both ends of the lips 507 are contained in a groove 508. However, the lips 501, 502 are superior to the lips 507 in generating a small torque.
When a sealing plate 509 is incorporated as shown in FIG. 13(c), the outer peripheral diameter of a peripheral surface 403 on the side of the groove 508 opposite to the raceway on the outer peripheral surface 402 of the inner ring must be made smaller than the outer peripheral diameter of the peripheral surface 404 on the raceway side to allow the sealing plate 509 to be readily incorporated, and to prevent the bifurcated sealing lip 507 from being damaged. This difference in level on the stepped portion of the outer peripheral surface 402 requires more complex processing by a centerless grinder when the outer peripheral surface 402 of the inner ring is ground. In an idler bearing having such an inner ring configuration, as shown in FIG. 12, the bracket 300 fitted over the inner ring 401 is an unstable manner and may form a weak or inaccurately placed joint. Moreover, the large number of processing steps required increases production costs.
Another bearing, shown in FIG. 14, has been proposed wherein a sealing lip 602 is allowed to directly slidably contact the outer peripheral surface 601 of an inner ring 600 without the need for a groove in the outer peripheral surface 601. This makes processing of the inner ring much easier. However, grease can easily leak out and foreign matter may penetrate into the bearing, because the lip 602 is Y-shaped in cross section, as in the case of seals used for a water pump. As a result, this arrangement is unsuitable for practical use with an idler bearing.